1. Field of the Invention
The present invention relates to a stray field collector (SFC) pad and a bio-molecule sensing module using the same, and more particularly, to a SFC pad, in which probe or detection molecules are attached to a plurality of magnetic labels (magnetic particles or beads) and they are bonded to complementary molecules to enhance a stray field sensor signal of the magnetic labels remaining in the vicinity of the sensor, and a bio-molecule sensing module and a biochip using the same.
2. Description of Related Art
Since the late 1990s, a technology of a weak magnetic field sensor has become a promising technology to develop biochip sensors and biochips. As shown in FIG. 1, the basic idea behind a spintronic biosensor is to replace traditionally used fluorescent markers by magnetic labels for sensitive detection of biomolecules and measure stray fields of the magnetic labels, to thereby develop an automated signal measurement technology with enhanced resolution and sensitivity.
Here, FIG. 1 shows a conventional magnetic label and a sensing method for detecting bio-molecules using a magnetic biochip sensor, which is one of conventional technologies. The conventional configuration includes a biochip sensor 100, a glass or silicon substrate 110 on which the biochip sensor 100 is mounted, a protection layer 120 for protecting the sensor 100, and a super-paramagnetic magnetic label 130 which is laid on the protection layer 120.
When an external magnetic field Happ is applied, the magnetic label 130 is magnetized in a direction 140, and a stray field 150 is thus induced in a direction opposite to the direction of the external field. Therefore, the total effective magnetic field in the sensor decreases.
In an array type bio-molecule sensing technology of the aforementioned magnetic biochip method, the magnetic labels are immobilized and remain on a surface of the sensor by bonding of detection and probe molecules and the magnetic sensor senses the resultant stray field.
Meanwhile, in a membrane strip bio-molecule sensing technology of the conventional magnetic biochip technologies, the magnetic labels remain within a strip by bonding of detection and probe molecules and the magnetic sensor senses the resultant stray field.
In the array type and strip method, the detection of the magnetic label (stray field) is carried out by using different types of integrated magnetic sensors, and sensitivity of the sensor decreases with increase of sensor size when the number of the remaining label is constant. The stray field by a single magnetic label and the effective magnetic field acting on the sensor can be expressed by the following equation:
                                                                        H                eff                            =                                                H                  app                                -                                  H                                      stray                    ⁢                                                                                  ⁢                    1                                                                                                                          =                              k                ⁢                                                      χ                    ⁢                                                                                  ⁢                                          V                      label                                                                            4                    ⁢                    π                    ⁢                                                                                  ⁢                                          z                      3                                                                      ⁢                                  H                  app                                                                                        [                  Mathematical          ⁢                                          ⁢          Equation          ⁢                                          ⁢          1                ]            where, z is the normal distance between the center of the magnetic label and the sensor surface, k=Alabel/Asensor is the active coefficient depending on the sensor area Asensor and the projected label area Alabel, and χ and Vlabel are the magnetic mass susceptibility and volume of the magnetic label respectively.
That is, the conventional technology shown in FIG. 1 measures the bio-molecule magnetic labels such as magnetic nanoparticles/beads placed in the vicinity of the sensor using the magnetic sensor 100 to detect the bio-molecules. In the array type, immobilization and hybridization for the bio-molecules are carried out on the surface of the sensor 100 and the magnetic labels remain on the surface. In the membrane strip method, the immobilization and hybridization for the bio-molecules are carried out within the strip and the magnetic labels remain within the strip. In both cases, the sensor area becomes an active region for the detection of the magnetic labels and an average of the label stray field formed over the sensor area is measured.
However, the sensitivity of the sensor 100 decreases with the increase of the sensor size when the number of the remaining magnetic labels is constant. For a small sensor of a micrometer size, there is a limitation in a dynamic range of the label detection of the sensor 100 and a resolution problem of the sensor since the active region of the label that can affect the sensor is limited to a micrometer size.
Moreover, in statistic view point of the distribution of bio-molecules, since the presence of the bio-molecules is measured and determined by the presence of the label only in the vicinity of the sensor that is very tiny as compared to the whole sample volume, the detection in the tiny region alone cannot represent the representative characteristics of the whole sample volume and accuracy/precision of the detection is consequently not reliable.